Technical Abstract: Spiroplasma group XIV strain EC-1, isolated from the gut of a lampyrid beetle Ellychnia corrusca, was previously determined to be serologically indistinguishable, by spiroplasma deformation test, from several spiroplasmas from tabanid flies (including strains TC-1 and TS-1). Criteria for erecting a new species which includes all three strains have therefore been met. It was hypothesized that similarities among these strains reflect transmission among lampyrid beetles, in which the organisms could overwinter, and tabanid adults in which lateral transmission could occur in spring, summer and fall. This conjecture was investigated by RFLP analysis. Although spiroplasma strains EC-1 from E. corrusca, TC-1 from Tabanus calens, and several strains from T. sulcifrons could by distinquished genotypically by this technique, there was considerable similarity among the profiles. Similarly, serological profiles among lampyrid and tabanid spiroplasmas varied more widely in their profiles than would be expected if the isolates reflect a single biovar, supporting the possibility of lampyrid-tabanid transmission cycles, as well as yet to be discovered host relationships. Genotypic (RFLP) analysis may therefore be a companion to serology in elucidating spiroplasma diversity, and may provide clues to strain host range.